Method and device for the addition in droplet form of a liquid reducing agent into an exhaust gas line

ABSTRACT

A method and a device for the addition in droplet form of a liquid reducing agent to an exhaust gas line of an internal combustion engine, particularly to a rear end side of an exhaust gas treatment component, includes at least identifying at least one exhaust gas parameter during operation of the internal combustion engine, determining a size of a droplet of the reducing agent to be added as a function of an exhaust gas parameter, adjusting a first delivery pressure of the reducing agent toward the exhaust line as a function of the determined size of the droplet, and adding the reducing agent to the exhaust line with an adding unit. In this way, it can be achieved, in particular, that the end side of the exhaust gas treatment component is evenly wetted during operation of the internal combustion engine by using the droplets of the reducing agent.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation, under 35 U.S.C. §120, of copending International Application No. PCT/EP2009/065392, filed Nov. 18, 2009, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2008 063 488.3, filed Dec. 17, 2008; the prior applications are herewith incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method and a device for the addition, in droplet form, of a liquid reducing agent into an exhaust line of an internal combustion engine.

Exhaust-gas purification systems of internal combustion engines, in particular of diesel engines, use exhaust-gas treatment components for exhaust-gas purification in exhaust lines. The exhaust-gas treatment components at least intermittently require the supply of a reactant for correct operation. The exhaust-gas treatment components include, in particular, SCR catalytic converters, to which ammonia in pure or compound form, for example a urea solution, is supplied as a reducing agent for the selective catalytic reduction of nitrogen oxides. Furthermore, such elements are also oxidation-catalytic exhaust-gas treatment components to which hydrocarbon compounds (fuel) are supplied as a reducing agent for the purpose of heating the exhaust gas. The heating of the exhaust-gas flow is provided during a thermal soot regeneration of a particle filter or for the sulfur regeneration of nitrogen oxide storage catalytic converters.

In order to achieve highly effective exhaust-gas purification, it is sought to obtain as uniform a distribution and as fine an atomization as possible of the reducing agent over the cross section of the exhaust line.

Adding the reducing agent in a direction counter to the flow direction of the exhaust gas, as described in European Patent Application EP 1 890 016 A1, corresponding to U.S. Pat. No. 7,849,676, causes the higher relative speed of the reducing agent in relation to the exhaust-gas flow to result in a finer and better distribution of the reducing agent. The effect is additionally assisted by the impingement of the reducing agent on the outflow side of the exhaust-gas treatment component, because the impinging droplets of the reducing agent can be additionally atomized or can evaporate from the surfaces of the exhaust-gas treatment component directly into the exhaust-gas flow.

In that case, the distribution of the reducing agent over a cross section of the exhaust line and the impingement on an outflow side of an exhaust-gas treatment component is dependent significantly on the operating state of the internal combustion engine. At high flow speeds of the exhaust gas, a reducing agent finely atomized by an adding unit is quickly deflected, in such a way that an outflow side of an exhaust-gas treatment component is at least only partially impinged upon.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method and a device for the addition in droplet form of a liquid reducing agent into an exhaust gas line, which overcome the hereinafore-mentioned disadvantages and at least partially solve the highlighted problems of the heretofore-known methods and devices of this general type and with which, in particular, as uniform a distribution as possible of the reducing agent in an exhaust-gas flow is obtained, in particular at all operating points of an internal combustion engine, in order to thereby improve evaporation of the reducing agent.

With the foregoing and other objects in view there is provided, in accordance with the invention, a method for the addition, in droplet form, of a liquid reducing agent into an exhaust line of an internal combustion engine. The method comprises:

-   -   a) detecting at least one exhaust-gas parameter during operation         of the internal combustion engine;     -   b) determining a size of a droplet of the reducing agent to be         added as a function of the at least one exhaust-gas parameter;     -   c) setting a first delivery pressure of the reducing agent         flowing towards the exhaust line as a function of the determined         size of the droplet; and     -   d) adding the reducing agent into the exhaust line with an         adding unit.

The detection of an exhaust-gas parameter during the operation of the internal combustion engine may take place, in particular, through the use of sensors in the exhaust line and/or in the internal combustion engine and/or may, however, also be derived from the operating conditions of the internal combustion engine.

The size of a droplet of a reducing agent is dependent substantially on the delivery pressure of the reducing agent and on the construction of the nozzle opening of an adding unit and on the chemical composition and the physical state of the reducing agent itself. The size of a droplet determined in this case is, in particular, such that the droplet, with high probability, impinges on an end side of an exhaust-gas treatment component disposed, in particular, upstream of an adding unit of the reducing agent in the exhaust line, in such a way that an evaporation and/or a fine distribution of the reducing agent (in particular over the entire cross section of the exhaust line) is permitted. The size of the droplet influences the flight path of the droplet in the exhaust line. In particular, with increasing size of the droplet, the inertia of the droplet with respect to a deflection by the exhaust-gas flow also increases.

In this case, the size of the droplet of reducing agent to be added is set, in particular, by adjusting the first delivery pressure of the reducing agent in a reducing agent line. Therefore, the higher the first delivery pressure, for instance, the smaller the respectively generated droplet, for example.

In contrast to the general perception that, at higher exhaust gas speeds, the reducing agent should be supplied to the exhaust line at the highest possible pressure in order to cover as great a distance as possible counter to the flow direction of the exhaust gas in the direction of an end side of an exhaust-gas treatment component and impinge upon the latter, it is thus provided in this case that the pressure, in particular, be reduced at elevated exhaust gas speeds, in such a way that larger droplets are formed which are subjected to a correspondingly less intense deflection by the exhaust gas. As a result of the less intense deflection, the droplets also reach regions of the end side of an exhaust-gas treatment component which are spaced apart from the adding unit, on which end side the reducing agent can then evaporate. A desired distribution of the reducing agent over the cross section of an exhaust line can be set in this way. Accordingly, the addition of the reducing agent into the exhaust line through an adding unit takes place according to the setting of the first delivery pressure, in such a way that reducing agent droplets of a certain size are formed.

In accordance with another mode of the method of the invention, the addition of the liquid reducing agent takes place downstream of an exhaust-gas treatment component and counter to a flow direction of an exhaust gas in the exhaust line, and the size of a droplet is set in such a way that a uniform distribution of the reducing agent over an impingement region of the exhaust-gas treatment component is attained.

The addition of the liquid reducing agent counter to the flow direction of the exhaust gas results in a deflection and/or flaring of the jet of liquid reducing agent. This then causes the adding region, that is to say the area which is actually wetted, in the exhaust-gas treatment component as well, to be varied slightly even in steady-state operation of the addition. It may nevertheless occur, specifically in the case of exhaust-gas parameters remaining relatively constant, that the same region of the exhaust-gas treatment component is always provided with reducing agent. This may lead to local cooling of the exhaust-gas treatment component and/or to reduced effectiveness, because the exhaust-gas treatment component is already saturated with reducing agent and the reducing agent consequently cannot be stored or evaporated in the desired way. With the targeted influencing of the addition of the liquid reducing agent proposed above, a substantially uniform distribution of the reducing agent over the impingement region of the exhaust-gas treatment component is realized. The “impingement region” is to be regarded as that region of the end side of the exhaust-gas treatment component which can be reached by the adding unit or an individual nozzle under normal conditions during the operation of the internal combustion engine. If the entire end surface of the exhaust-gas treatment component can be reached with one nozzle, the impingement region corresponds to the end surface. Otherwise, the impingement area is generally a smaller partial region of the end surface. For the latter case, it is often provided for the adding unit to be constructed in such a way that the sum of all of the impingement regions in terms of area covers at least the area of the end surface, wherein if appropriate impingement regions of different nozzles may also overlap. The impingement region generally constitutes a “flared” region accessible by the adding unit. In order to determine the impingement region it is, for example, possible to supply liquid reducing agent to a nozzle under constant conditions, wherein the impingement region in which the reducing agent reaches the end side of the exhaust-gas treatment component under normal operating conditions of the internal combustion engine is determined. Consequently, the adding region constitutes that partial region which is actually wetted in a specific situation of the exhaust-gas parameters, and the impingement region constitutes that region which the adding regions can reach in different situations of the exhaust-gas parameters. Consequently, it is also proposed in this case that the variations of the adding region be utilized in order to seek as uniform as possible a distribution of the reducing agent over the (potential) impingement region of the exhaust-gas treatment component. In this case, the “uniform” distribution is to be understood, in particular, from a laterally averaged perspective. It is clear that the impingement region is provided with liquid reducing agent in a plurality of cycles. In this case, during the subsequent adding cycle, primarily those regions of the exhaust-gas treatment component should be wetted which have a relatively low amount of reducing agent in the impingement region. In this case, the storage capability of the exhaust-gas treatment component and/or the temperature thereof should also be taken into consideration, if appropriate.

As a result of the impingement of the reducing agent against the rear end side of an exhaust-gas treatment component, it is achieved that the reducing agent can evaporate from the surface of the exhaust-gas treatment component directly into the exhaust-gas flow. A continuous conversion of pollutants by the reducing agent or a continuous hydrolysis of the reducing agent is therefore possible despite a discontinuous addition of the reducing agent into the exhaust line. The amount of reducing agent to be supplied can be regulated through the use of the frequency of the addition of the reducing agent by the adding unit. Accordingly, an adapted supply of reducing agent with a low delivery pressure of the reducing agent—and therefore relatively low volume flow of the reducing agent—is possible for a simultaneously high exhaust-gas volume flow and correspondingly high demand for reducing agent.

In accordance with a further mode of the method of the invention, the exhaust-gas parameter is at least one exhaust-gas parameter from the group:

-   -   exhaust-gas volume flow,     -   exhaust-gas flow speed,     -   exhaust-gas mass flow,     -   exhaust-gas temperature,     -   exhaust-gas pressure.

If appropriate, an exhaust-gas parameter may also be derived from a plurality of relevant exhaust-gas parameters. The exhaust-gas parameters may be detected at preferred points of the exhaust line or of the internal combustion engine and converted through the use of controllers, which may be provided if appropriate, to the exhaust-gas parameter prevailing in the exhaust line at the position of the adding unit. An introduction of the reducing agent into the exhaust line is therefore determined in each case as a function of at least one exhaust-gas parameter of the exhaust gas.

In accordance with an added mode of the method of the invention, in step c), the first delivery pressure can be set between 3 bar and 25 bar, in particular between 3 and 10 bar. Such a pressure range is advantageous because the system components can be produced inexpensively for that range and correspondingly integrated into a motor vehicle at low expense. Furthermore, pumps having a volume flow adequate for this application are widely available for those pressure values, and can likewise be integrated into a motor vehicle at acceptable expense.

In accordance with an additional, advantageous mode of the method of the invention, during the addition of the reducing agent, at least one adding parameter from the following group is varied:

-   -   the delivery pressure,     -   the size of the droplet,     -   the adding region on the exhaust-gas treatment component,     -   an adding location of the reducing agent,     -   an adding direction of the reducing agent.

With regard to the possible variations mentioned above, it is self-evidently also possible for a plurality of the adding parameters to be varied or held constant during chronologically offset adding cycles. In particular, the adding parameters are triggered by corresponding actuating devices or control devices of the device, which is outside the exhaust gas, for delivering the reducing agent. In particular, a variation of the delivery pressure leads at the same time to the variation of the size of the droplets and/or of the adding region. If, for example, a plurality of nozzles is provided for wetting the exhaust-gas treatment component, the adding location of the reducing agent (location of the nozzle) can be varied by a corresponding actuation of the different nozzles. If movable, pivotable nozzles are provided in the adding unit, the adding direction can likewise be set in a targeted manner through the use of such a movement.

In accordance with yet another mode of the method of the invention, the method may also be enhanced in such a way that at least one adding parameter is varied while an exhaust-gas parameter is constant.

In this case, it is very particularly preferable for a slight variation of the delivery pressure to be realized in order to move the adding region of the droplets slightly in the case of long journeys or trips of the internal combustion engine with substantially constant exhaust-gas parameters. In this way, in particular, local cooling of the exhaust-gas treatment component in the adding region or dispensing region is avoided.

In accordance with yet a further, particularly preferred mode of the method of the invention, in step d), the addition takes place with a size of the droplets of between 10 μm and 200 μm Sauter mean diameter, in particular between 30 μm and 150 μm. In this case, the Sauter mean diameter is adefined as follows: if one were to form the entire volume of the particles (in this case the droplets) of a discharge or ballast into equal-sized balls, the overall surface area of which is equal to the overall surface area of the particles, then those particles would have the Sauter mean diameter as their diameter.

In this case, it has been found in numerous tests that, in a preferred embodiment of the adding unit as a four-holed nozzle and with AdBlue, that is to say a urea-water solution, as the reducing agent, a Sauter mean diameter of the droplets of 45 μm is attained with a first delivery pressure of 8 bar, whereas a Sauter mean diameter of 137 μm is obtained at 3 bar.

In accordance with yet an added, advantageous mode of the method of the invention, at least 60% of the droplets added in step d) have a size determined according to step b) or larger. The proportion is preferably even higher than 80% or even 92%. It is the aim of the method to generate, with a certain first delivery pressure, such a size of droplets in such a way that the droplets, taking into consideration exhaust-gas parameters, cover a certain distance counter to the flow direction of the exhaust gas when added counter to the flow direction of the exhaust gas, and therefore impinge, preferably distributed uniformly over the cross section of the exhaust line, upon an end surface of an exhaust-gas treatment component. Accordingly, through the use of this method, it is sought to generate droplets which have at least a certain size in such a way that at least the portion of droplets can cover a defined minimum distance.

In accordance with yet an additional mode of the invention, the addition of the reducing agent is carried out in such a way that, during the operation of the internal combustion engine, the end side of the exhaust-gas treatment component is uniformly wetted by the droplets of the reducing agent.

Specifically, in the case of very large end sides of the exhaust-gas treatment component, such as are encountered, for example, in exhaust systems of trucks, the addition of the liquid reducing agent should be realized targetedly in a desired manner over the entire end side. For this reason, it is proposed, in particular, that the strategies disclosed herein be used in order to ensure that a (time-averaged) uniform wetting of the (rear) end side takes place. In this respect, reference may be made in this case to the explanations regarding the uniform wetting of the impingement region.

With the objects of the invention in view, there is also provided a device for the addition of a liquid reducing agent in droplet form into an exhaust line. The device comprises a pump for delivering the reducing agent, an adding unit for introducing the reducing agent into the exhaust line, a reducing agent line fluidically connecting the pump to the adding unit, a pressure regulating valve and a pressure oscillation damper both disposed between the pump and the adding unit, and a control unit for controlling at least the pump, the adding unit and the pressure regulating valve.

The control unit serves, in particular, for regulating and/or controlling the components including the pump, the metering unit and the pressure regulating valve and, if appropriate, further components of the device or of the motor vehicle. In this case, the controller serves to set a certain size of the droplets of the liquid reducing agent at the adding unit for adding the reducing agent into the exhaust line by controlling a first delivery pressure.

The first delivery pressure is, in particular, the pressure at which the reducing agent should be dispensed through the adding unit into the exhaust line. The first delivery pressure is generated, for example, by virtue of a pump and a pressure regulating valve being correspondingly actuated. The pump preferably delivers continuously at a (constant, maximum) second delivery pressure which is then dissipated or reduced by the pressure regulating valve to the respective first delivery pressure. The second delivery pressure is a pressure which prevails in the reducing agent line and proceeding from which the first delivery pressure, which permits an addition of the liquid reducing agent with a certain size of the droplets, can be set.

In particular, the first delivery pressure is set in relation to a second delivery pressure prevailing in the reducing agent line by delivery and/or recirculation through the use of the pump or by opening the pressure regulating valve. It is also possible, in particular, for the first delivery pressure to be set through the addition of reducing agent into the exhaust line with the adding unit, without delivery by the pump. Then, an at least partial addition of the reducing agent with a relatively small size of the droplets (at a relatively high second delivery pressure in the reducing agent line) therefore takes place until the second delivery pressure has been dissipated or reduced to the first delivery pressure. In this embodiment, the addition of the size of the droplets determined in step b) of the method takes place only when the first delivery pressure is reached.

The device is, in particular, suitable for carrying out the method according to the invention.

The pressure regulating valve is thus provided, in particular, for setting the first delivery pressure corresponding to step c) of the method according to the invention.

A pressure oscillation damper is required in particular because, in the reducing agent line, in which a first delivery pressure is set in order to generate a droplet of a certain size, pressure oscillations occur during operation of the internal combustion engine and during the dispensing of reducing agent from the adding unit. This is dependent, in particular, on a quantity being dispensed from the adding unit and secondly on the delivery rate of the pump and the delivery mode thereof (continuous or discontinuous). Furthermore, the first delivery pressure is influenced by a pressure regulating valve in that, when a certain pressure in the reducing agent line is exceeded, or to set the first delivery pressure, a reducing agent is recirculated in particular through a return line into a reducing agent tank. Pressure oscillations may also arise as a result of discontinuous opening and closing movements of a nozzle of the adding unit. In this way, pressure oscillations may also be formed which flow in the manner of waves through the reducing agent line.

The pressure oscillation damper thus serves, in particular, to keep the first delivery pressure set in the reducing agent line in order to add droplets of a certain size as constant as possible, or to approximate the second delivery pressure present in the reducing agent line to the first delivery pressure (determined in step c)). Fluctuations of the first delivery pressure are therefore reduced or prevented. In this case, it is particularly advantageous for the second delivery pressure upstream of the adding unit or in the reducing agent line in step d) to deviate from the first delivery pressure determined in step c) and to be set or adjusted only by at most 10%, in particular only by 5%, during the operation of the internal combustion engine. Therefore, if the adding unit opens to the exhaust line at a time at which the first delivery pressure has not been reached as a result of fluctuations of the pressure in the reducing agent line, the addition therefore takes place at a second delivery pressure. As a result of the reduction of the oscillations of the pressure in the reducing agent line by the pressure oscillation damper, the reducing agent is then added into the exhaust line with a second delivery pressure substantially approximated to the first delivery pressure.

In accordance with another feature of the device of the invention, the control unit is connected to at least one exhaust-gas sensor for determining at least one exhaust-gas parameter including, in particular, the exhaust-gas parameters already mentioned in the description of the method. The control unit thus also serves, in particular, to set at least one first delivery pressure in the reducing agent line which pressure is suitable for generating droplets of a size that can be transferred into the exhaust line by the adding unit and can then cover a minimum travel counter to the flow direction of the exhaust gas, in particular in order to impinge on an end side of an exhaust-gas treatment unit in the exhaust line. The size of the droplets is adapted in such a way that as uniform as possible a distribution of the reducing agent over the entire cross section of the exhaust line is obtained on that end side.

In accordance with a further advantageous feature of the invention, the exhaust-gas sensor for determining at least one exhaust-gas parameter is disposed on the air supply side of an internal combustion engine. The exhaust-gas parameters are therefore derived from parameters on the intake side of the internal combustion engine. In particular, the exhaust-gas sensor may be constructed in this case as a mass flow sensor or as a vacuum sensor. In particular, a detection signal of an exhaust-gas sensor is combined with parameters of the internal combustion engine, for example with the rotational speed of the internal combustion engine.

In accordance with an added feature of the invention, the adding unit may also include at least a multiplicity of nozzles or at least one movable nozzle.

It is self-evidently also possible for an adding unit to be provided in which a plurality of nozzles is provided, at least one of which is constructed to be movable, in particular pivotable. In the case of a multiplicity of nozzles, the configuration should be selected in such a way that the nozzles reach the entire end surface of the exhaust-gas treatment component, that is to say the sum of the impingement regions covers at least the end surface. For this purpose, a plurality of nozzles, for example three, four or five nozzles, may be disposed over the circumference of the exhaust line or the rear end side of the exhaust-gas treatment component. If a movable nozzle is provided, a corresponding gas-tight bearing and an adjusting motor will be required.

In accordance with a concomitant feature of the invention, it is particularly advantageous for the control unit of the device according to the invention to be configured to carry out the method according to the invention, and furthermore for the device and/or the method to be provided, in particular, for use in a motor vehicle.

The method and the device preferably relate to the addition of a liquid urea-water solution, wherein the exhaust-gas treatment unit has a hydrolysis coating at least on a section of an end side situated opposite the adding unit.

Other features which are considered as characteristic for the invention are set forth in the appended claims, noting that the features specified in the dependent claims may be combined with one another in any desired technologically meaningful way and define further embodiments of the invention.

Although the invention is illustrated and described herein as embodied in a method and a device for the addition in droplet form of a liquid reducing agent into an exhaust gas line, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, plan view of a motor vehicle having a device according to the invention;

FIG. 2 is an enlarged, plan view of a portion of an exhaust line during operation of the motor vehicle;

FIG. 3 is a view similar to FIG. 2 of a further embodiment of the device in a motor vehicle; and

FIG. 4 is a diagram illustrating a varying addition of reducing agent.

DETAILED DESCRIPTION OF THE INVENTION

Referring now in detail to the figures of the drawing, in which the same reference numerals are used for identical objects for explaining the invention and the technical field in more detail by showing particularly preferred structural variants to which the invention is not restricted, and first, particularly, to FIG. 1 thereof, there is seen a device 12 in a motor vehicle 21 having an internal combustion engine 3. In this case, an exhaust line 2 is provided which has at least one exhaust-gas treatment component 17 with a first end side 18 and a second end side 19. The exhaust-gas treatment component is traversed by an exhaust gas in a flow direction 20 from the first end side 18 to the second end side 19. In this case, an adding unit 8 of the device 12 is disposed downstream of the second end side 19 of the exhaust-gas treatment component 17. The adding unit 8 is positioned in such a way that a reducing agent supplied by the adding unit 8 at least partially impinges on the second end side 19 of the exhaust-gas treatment component 17, counter to the flow direction 20 of the exhaust gas in the exhaust line 2. Droplets of a certain size are provided for this purpose by the device 12. The droplets are supplied into the exhaust line 2 counter to the flow direction 20 of the exhaust gas and accordingly impinge at least partially on the second end side 19 of the exhaust-gas treatment component 17. The device 12 includes a reducing agent tank 22, a pump 10, a pressure oscillation damper 9, a pressure regulating valve 14 and the adding unit 8, which are connected to one another by a reducing agent line 13. Furthermore, exhaust-gas sensors 16 are provided at different points along the exhaust line 2 or at lines leading to an air supply side 25 of the internal combustion engine 3. The exhaust-gas sensors, in particular, transmit different exhaust-gas parameters 4 to a control unit 15. It is possible to also determine exhaust-gas parameters 4 in the exhaust line 2 by determining an air mass flow (or by determining the latter from a vacuum in the line and a rotational speed of the internal combustion engine 3), through the use of the exhaust-gas sensors 16 on the air supply side 25 of the internal combustion engine. The control unit 15 is furthermore connected at least to the pump 10 of the pressure regulating valves 14 and to the adding unit 8. The pressure regulating valve 14 may furthermore, in particular, be connected to a return line through which reducing agent can be returned from the reducing agent line 13 into the tank 22.

FIG. 2 shows a portion of the exhaust line 2 with an exhaust-gas treatment component 17 which has a first end side 18 and a second end side 19 and which is traversed by an exhaust gas in a flow direction 20 from the first end side 18 to the second end side 19. In this case, the exhaust gas may, if appropriate, have different exhaust-gas parameters 4 (for example exhaust-gas temperature, exhaust-gas speed, etc.) at different points of the exhaust line 2. Those exhaust-gas parameters are detected by exhaust-gas sensors 16. The adding unit 8, which is disposed downstream of the exhaust-gas treatment component 17, dispenses a reducing agent 1 in the form of droplets 6 preferably onto the second end side 19 of the exhaust-gas treatment unit 17. The droplets 6 of the reducing agent 1 are distributed preferably uniformly over an entire cross section 24 of the exhaust line, in particular uniformly over the largest possible cross section 24 which can be reached by the reducing agent 1.

FIG. 3 shows a further embodiment of the device 12 in a motor vehicle. In this case, a droplet 6 with a size 5 is supplied into the exhaust line 2 downstream of an exhaust-gas treatment component 17 with a first end side 18 and a second end side 19. The droplet 6 is dispensed by the adding unit 8 into the exhaust line 2 and moves along a droplet path 23. The droplet path 23 is influenced substantially by exhaust-gas parameters 4. Therefore, the device 12 sets a first delivery pressure 7 in the reducing agent line 13 in such a way that certain sizes 5 of the droplets 6 can preferably be generated which permit an impingement of the droplets 6 on the second end side 19 of the exhaust-gas treatment component 17. Data which are required for the detection of the exhaust-gas parameters 4 are gathered through the use of the exhaust-gas sensors 16 which may be disposed either downstream of the exhaust-gas treatment component 17 or upstream thereof or within the exhaust-gas treatment component 17. The exhaust-gas sensors 16 transmit their data over control lines or wirelessly to a controller 15 which is also connected at least to the adding unit 8, to a pressure regulating valve 14 and to a pump 10. The device 12 not only has the adding unit 8 but also a reducing agent tank 22, the pump 10, a pressure oscillation damper 9 and the pressure regulating valve 14, which are connected to one another by a reducing agent line 13. The control unit 15 determines the first delivery pressure 7 in the reducing agent line 13. Fluctuations in the respectively set first delivery pressure 7 may occur during operation of the device 12. The actual pressure in the reducing agent line 13 is referred to as a second delivery pressure 11, which is correspondingly controlled so as to deviate as little as possible from the first delivery pressure 7. The reducing agent 1 leaves the adding unit 8 at the second delivery pressure 11, which corresponds as closely as possible to the first delivery pressure 7.

FIG. 4 shows a rear view of an exhaust-gas treatment component 17. Four nozzles 29 are provided over the circumference of the exhaust line 2, downstream of the exhaust-gas treatment component 17. The nozzles 29 permit uniform wetting of the exhaust-gas treatment component 17 with liquid reducing agent, through the use of the control unit 15. Consequently, the adding unit is formed with four nozzles 29 in this case. The nozzles 29 are rigidly connected, although that is not imperatively necessary. A nozzle 29 disposed at the top of FIG. 4 is constructed to be movable or pivotable (see the double arrow). It is also shown that the same nozzle 29 may be assigned a separate impingement region 26 for liquid reducing agent, which is indicated by a corresponding dash-dotted line.

It is also shown in the lower region of FIG. 4 how a nozzle can uniformly reach an impingement region 26 which is reachable under the normal operating conditions of the internal combustion engine through the use of a targeted variation or modulation of an adding strategy. In this case, the lower nozzle constitutes an adding location 27 presently under consideration. Proceeding from the adding location 27, the impingement region 26 (marked by a darkened area) can be uniformly wetted by virtue of modulating adding regions 30 (indicated by dashed lines). In this case, an adding region 30 constitutes an impingement area of liquid reducing agent during an adding cycle. It can be seen that, in order to cover the entire impingement region 26, the shape and/or size of the adding region 30 and/or an adding direction 28 is varied. It can be seen that the entire impingement region 26 can be substantially uniformly sprayed with reducing agent, for example through the use of five adding cycles. In this case, it is not necessary for all of the adding regions 30 to all actually be disposed adjacent one another and/or for all of the adding regions 30 to be wetted with the same amount of reducing agent and/or with the same frequency. In fact, the exhaust-gas parameters and/or the storage and evaporation behavior of the exhaust-gas treatment component 17 must also be taken into consideration in this case. In general, a higher storage capacity and/or evaporation capacity is encountered in the central region of the exhaust-gas treatment component 17 due to the higher temperatures in the exhaust gas in that region and/or the more intensive flow through the exhaust-gas treatment component 17. This may also be taken into consideration in the adding strategy.

The modulation of the adding regions 30 takes place in a targeted manner, for example by the influencing of the delivery pressure in the respective reducing agent lines through corresponding regulation of the control unit 15. Superposed thereon are the exhaust-gas parameters, which result in a deflection or broadening or variation of the adding region 30. This is, however, preferably taken into consideration or compensated in the adding strategy. 

1. A method for the addition, in droplet form, of a liquid reducing agent into an exhaust line of an internal combustion engine, the method comprising the following steps: a) detecting at least one exhaust-gas parameter during operation of the internal combustion engine; b) determining a size of a droplet of the reducing agent to be added as a function of the at least one exhaust-gas parameter; c) setting a first delivery pressure of the reducing agent flowing towards the exhaust line as a function of the determined size of the droplet; and d) adding the reducing agent into the exhaust line with an adding unit.
 2. The method according to claim 1, which further comprises: providing an exhaust-gas treatment component having an impingement region; carrying out the step of adding the liquid reducing agent downstream of the exhaust-gas treatment component and counter to a flow direction of an exhaust gas in the exhaust line; and setting the size of the droplet to attain a uniform distribution of the reducing agent over the impingement region of the exhaust-gas treatment component.
 3. The method according to claim 1, wherein the at least one exhaust-gas parameter includes at least one exhaust-gas parameter selected from the group consisting of: exhaust-gas volume flow; exhaust-gas flow speed; exhaust-gas mass flow; exhaust-gas temperature; and exhaust-gas pressure.
 4. The method according to claim 1, which further comprises setting the first delivery pressure in step c) to be between 3 bar and 25 bar.
 5. The method according to claim 1, which further comprises, during the step of adding the reducing agent, varying at least one adding parameter selected from the group consisting of: the delivery pressure; the size of the droplet; an adding region on an exhaust-gas treatment component; an adding location of the reducing agent; and an adding direction of the reducing agent.
 6. The method according to claim 5, which further comprises varying at least one adding parameter while keeping an exhaust-gas parameter constant.
 7. The method according to claim 1, which further comprises carrying out the step of adding the reducing agent in step d) with the size of the droplet being between 10 μm and 200 μm Sauter mean diameter.
 8. The method according to claim 1, which further comprises providing at least 60% of the droplets added in step d) with a size determined according to step b) or larger.
 9. The method according to claim 1, which further comprises: providing an exhaust-gas treatment component having an end side; and carrying out the step of adding the reducing agent by uniformly wetting the end side of the exhaust-gas treatment component with droplets of the reducing agent during operation of the internal combustion engine.
 10. A device for the addition of a liquid reducing agent in droplet form into an exhaust line, the device comprising: a pump for delivering the reducing agent; an adding unit for introducing the reducing agent into the exhaust line; a reducing agent line fluidically connecting said pump to said adding unit; a pressure regulating valve and a pressure oscillation damper both disposed between said pump and said adding unit; and a control unit for controlling at least said pump, said adding unit and said pressure regulating valve.
 11. The device according to claim 10, which further comprises at least one exhaust-gas sensor for determining at least one exhaust-gas parameter, said at least one exhaust-gas sensor connected to said control unit.
 12. The device according to claim 11, wherein said exhaust-gas sensor for determining at least one exhaust-gas parameter is disposed on an air supply side of an internal combustion engine.
 13. The device according to claim 10, wherein said adding unit includes at least a multiplicity of nozzles.
 14. The device according to claim 10, wherein said adding unit includes at least one movable nozzle.
 15. The device according to claim 10, wherein said control unit is programmed to carry out the method according to claim
 1. 